Clouds and contrails are completely different. I covered this in my last post. Clouds form at ground level. They need DIRTY air with lots of sub-micron particles to act as condensation nuclei and high humidity in the range of 60-70%.

Wrong. Cirrus clouds form in the upper troposphere.

Quote:

Unmodified jet exhaust should not contain enough particulate matter to form a cloud and it would be impossible in low-humidity environments where chemtrails are often spotted.

And what is the basis of your claim that the upper troposphere is a low-humidity environment? (hint: it's that pesky ice supersaturation isue again)

Once ice crystals start to form in a contrail stream, they will grow untill they splinter and fracture. In this manner, the crystals propagate and multiply.